2. Introduction
From an engineering viewpoint, the
ground beneath a site can conveniently
be divided into the categories, based
upon generalizations of its expected
behaviour in construction works.
Soil used to be rock, which was tuned
into soil by weathering, chemical and
mechanical forces.
Nature recycles the soil to rock, that this
takes millions of years.
4. HORIZONS
Surface horizon is usually referred to as
the O layer. It consists of loose organic
matter such as fallen leaves and other
biomass.
Below is the A horizon, containing a
mixture organic mineral materials and
organics.
5. HORIZONS
Next is E horizons, layer from which clays,
iron and aluminum oxides have been lost
by leaching process
Below horizons E is B, which most of the
iron, clays, and other leached materials
have accumulated.
After that is C horizons consisting of
partially weather bedrock
And last is R horizons of hard bedrock
6. SOIL
Three main size groups :
Sand (0.05 to 2.00 mm)
Silt (0.002 to 0.05 mm)
Clay ( less than 0.002 mm
8. COLOR
Soils come in a wide range of colors.
Shades of brown, red, orange, yellow,
gray and even blue or green.
A dark color usually indicates the
presence of organic matter.
9. TEXTURE
A soil texture depends on its content of the
three main mineral components of the soil,
sand ,silt and clay.
Very fine textured soils may be poorly
drained.
Medium texture and a relatively even
proportion of all particle sizes are most
versatile
10. AGGREGATION
Individual soil particles tend to be bound
together into lager units referred to as
aggregates or soil peds.
Aggregation occurs as a result of complex
chemical forces acting an small soil
components in soil act as glue binding
particles together.
11. POROSITY
Part of the soil that is not solid is made up
pores of various sizes and shapes
Porosity greatly affects water movement
and gas exchange.
12. ION CONTENT
Particularly the clay, hold groupings of
atoms known as ions.
These ions carry a negative charge.
Like magnets, these negative ions
(anions) attract positive ions (cations)
13. pH
Another important chemical measured is
soil pH.
Refers to the soil acidity or alkalinity.
A greater concentration of hydrogen
results in a lower pH, meaning greater
acidity
18. Soil Investigation
Specifically related to the subsoil
beneath the site under investigation
and could be part of or separate from
the site investigation
A well designed soil investigation can
often lead to project cost savings in
the long term by allowing contractors
to foresee potential problems.
19. Purpose
1. Determine the suitability of the site for
the proposed project.
2. Determine an adequate and economic
foundation design.
3. Determine the difficulties which may
arise during the construction process
and period.
4. Determine the occurrence and/or
cause of all changes in subsoil
conditions.
20. Soil Samples
1) Disturbed Soil Samples
Soil samples obtained from boreholes
and trial pits. The method of extraction
disturbs the natural structure for visual
grading, establishing the moisture
content and some lab tests. Disturbed
soil samples should be stored in
labelled air tight jars.
21. Soil Samples
2) Undisturbed Soil Samples
Soil samples obtained using coring tools which
preserve the natural structure and properties of
the subsoil. The extracted undisturbed soil
samples are labelled and laid in wooden boxes
for dispatch to a lab for test. This method of
obtaining soil samples is suitable for rock and
clay sub-soils but difficulties can be
experienced in trying to obtain undisturbed soil
samples in other types of subsoil.
22. Soil Investigation Methods
Method chosen will depend on several
factors:
1. Size of contract;
2. Type of proposed foundation;
3. Type of sample required;
4. Type of subsoils which may be
encountered.
23. Soil Investigation Methods
As a general guide the most suitable
methods in terms of investigation depth
are:
1. Foundations up to 3.000d – trial pits;
2. Foundations up to 30.000d –
borings;
3. Foundations over 30.000d – deep
boring and in-situ examination from
tunnels and/or deep pits.
24. Types Of Investigation
Generally the following soil investigation
techniques are employed for the majority of
projects:
Trial Pitting
Dynamic Probe Testing
Cable Percussive Boreholes
Rotary Drilled Boreholes
25. Trial Pitting
Trial pitting can be carried out by a
variety of methods from hand dug pits
to machine excavated trenches.
Trial pitting is generally carried out to a
maximum depth of 4.5m with standard
excavation plant and, depending on
soil conditions, is generally suitable for
most low rise developments.
26. Trial Pitting
All trial pit investigations are supervised by
experienced engineers with a thorough
understanding of geology and soil
mechanics.
27.
28.
29. Cable Percussive Boreholes
Suitable for most projects, cable
percussive boreholes are a common
method of site investigation.
Using a land rover towed rig or a specialist
cut down rig suited to restricted access
locations most sites can be investigated
30. Cable Percussive Boreholes
In-situ testing techniques including
Standard Penetration Testing,
Permeability Testing, Borehole Vane
Testing and Packer Testing can all be
carried out in the boreholes in order to
provide information for geotechnical
design
31. Cable Percussive Boreholes
Disturbed and undisturbed samples are
retrieved from the boreholes for inspection
and logging by engineers and subsequent
testing in a laboratories.
34. Operation of cable percussion rig for working in
areas of restricted access or with restricted
headroom
35. Rotary Drilled Boreholes
Rotary drilling techniques are
employed where boreholes are
required into very dense gravel or
bedrock.
Samples of bedrock are recovered in
seamless plastic tubes for subsequent
logging by a suitably qualified
engineer and for laboratory testing
36. Rotary Drilled Boreholes
Most of rotary coring work relies on the
use of drilling rigs which can also obtain
continuous samples of soils using
dynamic sampling equipment.
The rigs are suitable for limited access
works.
